Launchpad.net

CVE 2005-0337

Postfix 2.1.3, when /proc/net/if_inet6 is not available and permit_mx_backup is enabled in smtpd_recipient_restrictions, allows remote attackers to bypass e-mail restrictions and perform mail relaying by sending mail to an IPv6 hostname.

See the CVE page on Mitre.org for more details.